The Effects of Chronic Substance Misuse on the Auditory and Vestibular Systems: Preliminary Findings.

Objectives: Accumulating reports suggest that substance use disorders (SUDs) potentially lead to hearing and/or vestibular loss, particularly when overdose is involved. However, the existing literature is weak, consisting of case reports or small sample studies and that did not comprehensively evaluate both the auditory and vestibular systems. The objectives of this study were to determine the effect of chronic substance misuse on behavioral and physiological auditory and vestibular outcomes in adults with substance misuse histories (SUD group) as compared with an age- and sex-matched control group without substance misuse histories. We hypothesized that chronic substance misuse would negatively affect the auditory system, similar to known ototoxic medications, resulting in high-frequency sensorineural hearing loss, and the vestibular system, similar to acute effects of central-mediating medications, resulting in central abnormalities and imbalance.

Design: Data were analyzed for 60 adults with a substance misuse history (mean age, 42.2; range, 20 to 58 years) and 20 adults without (mean age, 37.2; range, 21 to 56 years). Outcome measures included responses on a health and substance-use questionnaire, the Montreal Cognitive Assessment screening, tympanometry, standard and extended high-frequency (EHF) pure-tone air-conduction thresholds, standard and EHF distortion product otoacoustic emissions, click-evoked auditory brainstem responses (ABRs), speech recognition in noise, oculomotor function, horizontal canal video head impulse test, cervical and ocular vestibular evoked myogenic potentials, and clinical dynamic visual acuity and standing balance tests.

Results: Most participants in the SUD group reported histories of polysubstance misuse. The SUD group had significantly poorer Montreal Cognitive Assessment screening scores than the control group. There was no significant difference between groups for the presence of middle-ear status. Although most thresholds were within the normal range, mean audiometric thresholds were significantly poorer for both the standard and EHF ranges for the SUD group compared with the control group. These patterns held even after adjusting for smoking and noise exposure. Distortion product otoacoustic emission, ABR wave III, and ABR wave V amplitudes were significantly smaller for the SUD group than the control group, with no significant differences between groups for ABR waves III and V latencies, which suggests elevated thresholds from a cochlear origin. Mean speech recognition in noise was not significantly different between groups. There were statistically significant differences or associations between groups for oculomotor function and standing balance. Participants in the SUD group were significantly more likely to have abnormal oculomotor function and impaired tandem stance, even after adjusting for head trauma history. There was an effect of group on cervical vestibular evoked myogenic potential amplitudes; however, electromyography normalization could not be performed. There was no significant group effect on other peripheral vestibular measures, including video head impulse test gain and ocular vestibular evoked myogenic potential, and dynamic visual acuity, suggesting no significant impact on vestibular nerve function.

Conclusions: Our preliminary findings suggest negative impacts to hearing and vestibular function in people with chronic substance misuse histories. The auditory results do not align with classic ototoxicity effects, although further investigation is warranted in this area; the vestibular results are consistent with central medication effects, and substance misuse has differential influences on auditory and vestibular function. Results potentially warrant diagnostic monitoring for people with SUDs to reduce their communication barriers and fall risk.